1. Field of the Invention
This invention is in the field of treating paper webs to render them less permeable by liquids while retaining their porosity and strength characteristics.
2. Description of the Prior Art
There have been some disclosures in prior patents regarding the treatment of various materials with organic silicon compounds in order to render them water repellent. For example, in U.S. Pat. No. 2,306,222 to Patnode, there is a disclosure of treating various materials, including paper, with an organo-silicon halide such as methyl silicon chloride in vapor form to render the body water repellent. It was hypothesized that the organo-silicon halide vapors react with an absorbed film of water to form the corresponding silicol which is strongly absorbed and water repellent, or results in the formation of a water repellent silicone.
U.S. Pat. No. 2,386,259 to Norton refers to the treatment of fabrics or paper to make them water repellent by treating such materials with the product obtained by the hydrolysis of a methyldihalogensilane.
Norton in U.S. Pat. No. 2,412,470 described a process for treating a solid body to render it water repellent which involved treating the same with a mixture containing about 2.8 to 99.2% by weight of trimethyl silicon chloride and about 97.2 to 0.8% by weight of silicon tetrachloride.
U.S. Pat. No. 2,961,338 to Robbart refers to a process of treating wool to render the same water repellent by reacting the same with an organo silicon halide in vapor form while the wool is at a relatively low moisture content.
Robbart in U.S. Pat. No. 2,995,470 described a continuous process for treating material with vapors of a waterproofing substance such as an organo silicon halide wherein vapors of the treating reagent mixed with an inert carrier gas were introduced into an enclosed treating zone while a length of the material to be treated was passed continuously through the zone. Downstream from the reaction zone the spent vapors, including the by-products, were exhausted from the system. The objective here was to remove the by-products as rapidly as possible so that they did not have an opportunity to build up appreciably in concentration.
In U.S. Pat. No. 3,856,558 Robbart suggested rendering cellulosic materials water repellent by contacting the same while they have a water content between 2 and 7 weight percent with vapors of a lower alkyl silicon halide which reacts with water to form a siloxane and maintaining the cellulosic material and halide in contact between 0.1 and 8 seconds. The conditions are such that the cellulosic material being contacted is rendered water repellent and has a pH greater than 2.5. The objective of this technique was to eliminate the subsequent step of neutralizing hydrogen chloride formed as a by-product of the alkyl silicon halide reaction with water.
Armbruster et al U.S. Pat. No. 4,170,690 suggested the use of a mixture of silanes to produce a coating composition which was said to impart abrasion resistance to thermoplastic substrates. The coating composition described therein contained about 30 to 50 parts by weight of a colloidal silica and about 50 to 70 parts by weight of a mixture of a dialkyldialkoxysilane and an alkyl trialkoxysilane with a weight ratio of about 1:19 to about 1:4 between the two. The coating compositions resulted in the production of gelled, impervious coatings which are not intended to be applied to a porous substrate such as paper.
While these disclosures appear in the prior art, the prior art has yet to come up with a method and composition for treating paper with silane solutions which are commercially acceptable. In those instances in which an alkyl silicon halide has been used, the disposition of the resulting hydrogen halide vapor has posed serious problems because of the corrosiveness of the vapor, the contamination of the atmosphere, and the weakening of the paper strength by its presence.